Water-based Conductive Ink Research Articles

Review on solvent- and surfactant-assisted water-based conductive inks for printed flexible electronics applications

Review on solvent- and surfactant-assisted water-based conductive inks for printed flexible electronics applications

Imperceptible liquid metal based tattoo for Human-Machine interface on hairy skin

Biopotential signals recorded by skin surface electrodes reflect the state of the body and corresponding organ functions. These signals are commonly utilized in clinical diagnosis, health monitoring, sports training, and human–computer interaction. However, the utilization of conventional electrodes on hairy skin causes a number of issues, including suboptimal skin compliance, obstructed sweat secretion and impaired tactile perception, making it difficult to obtain long-term and high-fidelity biopotential recordings. Here, we propose an imperceptible spray-on electrode tattoo (SE-tattoo) with sweat-permeability, high adhesiveness, high conductivity, and fast curing ability (<20 s). The water-based conductive ink is sprayed directly on the hairy skin to form a conformable conductive tattoo that neither affects nor is affected by the skin hair. We demonstrate it for heart health monitoring, sports training, electro-tactile display and close-loop teleoperation control. The SE-tattoo offers a reliable and versatile solution to biopotential recordings and serves as a promising platform for bidirectional human–machine interaction.One-Sentence Summary: Imperceptible sweat-permeable SE-tattoo enables high-fidelity biopotential recordings for bidirectional human–machine interaction.

Ground-state electron transfer in all-polymer donor:acceptor blends enables aqueous processing of water-insoluble conjugated polymers

Water-based conductive inks are vital for the sustainable manufacturing and widespread adoption of organic electronic devices. Traditional methods to produce waterborne conductive polymers involve modifying their backbone with hydrophilic side chains or using surfactants to form and stabilize aqueous nanoparticle dispersions. However, these chemical approaches are not always feasible and can lead to poor material/device performance. Here, we demonstrate that ground-state electron transfer (GSET) between donor and acceptor polymers allows the processing of water-insoluble polymers from water. This approach enables macromolecular charge-transfer salts with 10,000× higher electrical conductivities than pristine polymers, low work function, and excellent thermal/solvent stability. These waterborne conductive films have technological implications for realizing high-performance organic solar cells, with efficiency and stability superior to conventional metal oxide electron transport layers, and organic electrochemical neurons with biorealistic firing frequency. Our findings demonstrate that GSET offers a promising avenue to develop water-based conductive inks for various applications in organic electronics.

Screen-printed water-based conductive ink on stretchable fabric for wearable micro-supercapacitor

Micro-supercapacitors (MSCs) have received a lot of attention with the rapid development of wearable, highly integrated, and flexible electronics due to their high power density and long cycle life. Among the preparation methods, screen printing is widely used due to its simplicity, low cost, integratability, and ease of industrial production. However, the conductivity, rheology, and printability of the ink are still required to be further optimized in order to improve the resolution and electrochemical properties of the printed patterns. And combining a high energy capacity and wearability of MSCs is also a big challenge. Therefore, a green and environmentally friendly water-based conductive ink is prepared herein to develop a CO-CNT-MnO2-based micro-electrode on stretchable cotton/spandex fabric by screen printing. The CO-CNT-MnO2/F-based MSCs with a forked finger structure are further assembled combined with PVA/LiCl, and high electrochemical performance of the assembled device due to the synergy of double layer capacitance and pseudocapacitor capacitance storage could be achieved as an area capacitance of 8.479 mF/cm2 at 10 mV/s and reach maximum energy density of 0.132 mWh/cm2 at power density of 0.176 mW/cm2. In addition, the assembled MSCs still have high capacitance retention under stretching/folding/bending/friction conditions. This work highlights the great potential of the new water-based conductive ink for the application of stretchable MSCs based on screen printing.

Effect of natural surfactant on the performance of reduced graphene oxide conductive ink

Conductive ink with stable dispersion and excellent printing properties can be produced using graphene-based nanomaterials and suitable solvents for flexible printed electronics applications. Eco-friendly water-based inks can be used as an alternative to organic solvents-based inks to minimize environmental impacts. Graphene oxide (GO) nanofillers can form stable aqueous dispersions and can be produced in bulk quantities using chemical exfoliation methods. Hence GO nanofillers can be used as a filler to produce water-based conductive ink for printed electronics applications. However, the higher surface tension and lower stability are major drawbacks which limit its printing properties. Natural surfactants can minimize these issues to ensure smooth printing with a higher shelf life as compared to harmful synthetic surfactants. This study aimed to investigate the role of natural-based surfactants such as gum arabic, cellulose nanocrystals and alkali lignin in producing stable and high performing water-based GO ink. The prepared ink samples were characterized for their wetting properties, printability, and storage time. The ink was also investigated for structural, functional groups, and stability. The printed patterns were investigated for morphological and electrical properties. The results from study indicate that the GO with alkali lignin surfactant gives long-term stability and better printing properties compared to other samples. The printed pattern after thermal reduction was found to have a conductivity of 833 S/m, which was reduced by only 2.6% after 100 bending cycles, whereas the electrical conductivity was reduced by only 0.6% after 10 rolling cycles indicating a great potential to be used in flexible electronic devices.

Conductive inks composed of multicomponent carbon nanomaterials and hydrophilic polymer binders for high-energy-density lithium-sulfur batteries

Lithium-sulfur (Li-S) battery research has been greatly advanced through designing sulfur host materials. However, the vast majority of these host materials are not yet used for the construction of high-energy-density batteries, due to the lack of effective ways to fabricate high-performance cathodes under high-sulfur-loading conditions. Here we present a convenient and universal strategy toward traditional slurry-coating procedure for fabricating high-sulfur-loading cathodes. Through rational designing conductive additives and polymer binders, their derived water-based conductive inks are developed to improve the mechanical and conductive properties of the slurry-coating cathodes and to reduce the polysulfide shuttling of the slurry-coating cathodes with high sulfur content (64–72 wt%) and high sulfur loading (>5 mg cm−2). This strategy not only enables the Super-P/S cathodes to deliver the enhanced structure parameters and electrochemical performance for constructing a 2.5 Ah pouch cell with a specific energy of 323 Wh kg−1, but also is suitable for diverse lab-developed sulfur hosts, thus opening a promising avenue for high-energy-density Li-S batteries.

Use of Nanocellulose to Produce Water-Based Conductive Inks with Ag NPs for Printed Electronics.

The need for more sustainable printed electronics has emerged in the past years. Due to this, the use of nanocellulose (NC) extracted from cellulose has recently been demonstrated to provide interesting materials such as functional inks and transparent flexible films due to its properties. Its high specific surface area together with the high content of reactive hydroxyl groups provide a highly tailorable surface chemistry with applications in ink formulations as a stabilizing, capping, binding and templating agent. Moreover, NC mechanical, physical and thermal properties (high strength, low porosity and high thermal stability, respectively) provide an excellent alternative for the currently used plastic films. In this work, we present a process for the production of water-based conductive inks that uses NC both as a template for silver nanoparticles (Ag NPs) formation and as an ink additive for ink formulation. The new inks present an electrical conductivity up to 2 × 106 S/m, which is in the range of current commercially available conductive inks. Finally, the new Ag NP/NC-based conductive inks have been tested to fabricate NFC antennas by screen-printing onto NC-coated paper, demonstrating to be operative.

Novel eco-friendly water-based conductive ink for the preparation of disposable screen-printed electrodes for sensing and biosensing applications

This paper presents a novel water-based conductive ink obtained by proper combination of chitosan (C) biopolymer, graphite (G) powder, and glycerol (G), and its subsequent use in the screen-printing of disposable electrodes on polyethylene terephthalate (PET) plastic obtained from recyclable soda bottles (CGG/PET electrodes). The electrode was used in two directions, as a sensor for the quantification of uric acid and as a biosensor for the enzymatic quantification of catechol. The linear sweep voltammetry-detection of uric acid (UA), showed a linear range between 8.0 and 500 μmol L−1 and a limit of detection (LOD) of 0.36 μmol L−1. Additionally, the performance of the resulting electrodes for biosensing purposes was evaluated through the development of a catechol biosensor by the modification of the GCG/PET surface with the tyrosinase (Tyr) enzyme, multiwalled carbon nanotubes (MWCNTs), and dyhexadecyl phosphate (DHP) (Tyr-MWCNT-CGG/PET). Using the chronoamperometry technique a linear relationship from 0.5 to 50 μmol L−1 and LOD of 0.3 μmol L−1 were achivied for catechol. The proposed electrode has demonstrated outstanding analytical characteristics, proving its potential as a disposable, low-cost, and environmentally friendly platform for electrochemical sensing and biosensing purposes.

Preparation and application of water-based nano-silver conductive ink in paper-based 3D printing

PurposeIn flexible electronics applications, organic inks are mostly used for inkjet printing. Three-dimensional (3 D) printing technology has the advantages of low cost, high speed and good precision in modern electronic printing. The purpose of this study is to solve the high cost of traditional printing and the pollution emissions of organic ink. It is necessary to develop a water-based conductive ink that is easily degradable and can be 3 D printed. A nano-silver ink printed circuit pattern with high precision, high conductivity and good mechanical properties is a promising strategy.Design/methodology/approachThe researched nano-silver conductive ink is mainly composed of silver nanoparticles and resin. The effect of adding methyl cellulose on the ink was also explored. A simple 3 D circuit pattern was printed on photographic paper. The line width, line length, line thickness and conductivity of the printed circuit were tested. The influence of sintering temperature and sintering time on pattern resistivity was studied. The relationship between circuit pattern bending performance and electrical conductivity is analyzed.FindingsThe experimental results show that the ink has the characteristics of low silver content and good environmental protection effect. The printing feasibility of 3 D printing circuit patterns on paper substrates was confirmed. The best printing temperature is 160°C–180°C, and the best sintering time is 30 min. The circuit pattern can be folded 120°, and the cycle is folded more than 60 times. The minimum resistivity of the circuit pattern is 6.07 µΩ·cm. Methyl cellulose can control the viscosity of the ink. The mechanical properties of the pattern have been improved. The printing method of 3 D printing can significantly reduce the sintering time and temperature of the conductive ink. These findings may provide innovation for the flexible electronics industry and pave the way for alternatives to cost-effective solutions.Originality/valueIn this study, direct ink writing technology was used to print circuit patterns on paper substrates. This process is simple and convenient and can control the thickness of the ink layer. The ink material is nonpolluting to the environment. Nano-silver ink has suitable viscosity and pH value. It can meet the requirements of pneumatic 3 D printers. The method has the characteristics of simple process, fast forming, low cost and high environmental friendliness.

Surfactant-assisted water-based graphene conductive inks for flexible electronic applications

BackgroundInkjet printing of graphene conductive inks plays a critical role in the technological advancement in flexible and stretchable electronics applications. In this study, water-based graphene conductive ink was fabricated and printed through inkjet printing on polyethylene terephthalate substrate. MethodsDeionized (DI) water and three different types of surfactants (sodium dodecyl sulfate (SDS), polyvinylpyrrolidone (PVP), and Gum Arabic GA)) were utilized in the preparation of graphene conductive inks. Significant FindingAmong other conductive ink formulations, graphene conductive inks fabricated using the DI/PVP surfactant exhibit relatively higher wetting and stability properties. In addition, this formulation led to an increment of about 80% in electrical conductivity compared to DI water-based conductive ink. The results revealed an improvement of about 50 times in the electrical conductivity of the printed film when the number of the printing cycle was increased from 1 to 10. Furthermore, it was observed that under 50% tensile strain, the graphene film prepared using the PVP surfactant exhibited only a 0.12% drop in electrical conductivity. Therefore, it is inferred that the conductive inks prepared from DI/PVP surfactants are highly suitable for use in flexible and wearable electronics.

Development of environmentally friendly inkjet printable carbon nanotube‐based conductive ink for flexible sensors: effects of concentration and functionalization

The fabrication of environmentally friendly printed flexible sensors is still an emerging technology, but with vast potential applications. Among the available printing techniques, inkjet printing is considered as a promising technique for flexible electronics because it enables high volume and versatile manufacturing, at low environmental impact. This study demonstrates a simple and facile method of preparing an environmentally benign water-based conductive ink, by dispersing functionalized and non-functionalized multi-walled carbon nanotubes (MWCNTs) in aqueous solution with the help of a biopolymer surfactant. The concentration of CNTs in the ink formulation was varied from 0.25 to 0.75 wt%, and additives such as triton-x 100, polypropylene glycol, and defoamer were added to achieve desirable ink properties. Inkjet printable ink was produced, and it was observed that the conductivity of the printed pattern is dependent on the printing pass. In addition, it was found that as the number of printing layer increases, there is higher synergy between concentration and number of printing pass in F-MWCNTs printed ink to produce higher electrical conductivity, compared to MWCNTs printed ink. Generally, the findings of this study could potentially open opportunities for global economic growth through the applications of printed, low cost and environmentally friendly flexible sensors.

Flexible Electronics Directly Written with an Ultrastable Ballpoint Pen Based on a Graphene Nanosheets/MWCNTs/Carbon Black Nanocomposite

A writable ultrafine water-based conductive ink with excellent stability and no harmful gas emission was prepared. The mass fraction of carbon conductive particles was 4.95%, and the mean median pa...

Sensitive piezoresistive sensors using ink-modified plant fiber sponges

With increasing demand for wearable electronics, highly sensitive and flexible piezoresistive sensors (PRS) have received increasing attention. As an important component, structural materials with high compressibility and electrical conductivity are a powerful impetus for the development of PRS. Since the structural deformation occurred during high-temperature carbonization makes many three-dimensional porous structures made from low-cost biomass unsuitable for fabricating flexible PRS, we propose a convenient carbonization-free route to prepare PRS devices based on natural plant fibers. By developing and using a water-based conductive ink, the surface modification and assembly of plant fibers can be integrated into a one-pot foaming process to generate ink-modified plant fiber sponges (m-PFS). Benefiting from favorable mechanical property and sensitivity (133.3 kPa−1 in a pressure range of 10 ~ 750 Pa), the polydimethylsiloxane packaged m-PFS is demonstrated as a high-performance flexible PRS for detecting human physiological signals. This study provides new opportunities for the application of biomass in wearable electronics and human health monitoring.

Solution-Processed Sensing Textiles with Adjustable Sensitivity and Linear Detection Range Enabled by Twisting Structure.

Wearable strain sensors are emerging rapidly for their promising applications in human motion detection for diagnosis, healthcare, training instruction, and rehabilitation exercise assessment. However, it remains a bottleneck in gaining comfortable and breathable devices with the features of high sensitivity, linear response, and tunable detection range. Textiles possess fascinating advantages of good breathability, aesthetic property, tailorability, and excellent mechanical compliance to conformably attach to human body. As the meandering loops in a textile can be extended in different directions, it provides plenty of room for exploring ideal sensors by tuning a twisting structure with rationally selected yarn materials. Herein, textile sensors with twisting architecture are designed via a solution-based process by using a stable water-based conductive ink that is composed of polypyrrole/polyvinyl alcohol nanoparticles with a mean diameter of 50 nm. Depending on the predesigned twisting models, the thus-fabricated textile sensors show adjustable performances, exhibiting a high sensitivity of 38.9 with good linearity and a broad detection range of 200%. Such sensors can be integrated into fabrics and conformably attached to skin for monitoring subtle (facial expressions, breathing, and speaking) and large (stretching, jumping, running and jogging, and sign language) human motions. As a proof-of-concept application, by integrating with a wireless transmitter, the signals detected by our sensors during exercise (e.g., running) can be remotely received and displayed on a smartphone. It is believed that the integration of our textile sensors with selected twisting models into a cloth promises full-range motion detection for wearable electronics and human-machine interfaces.

Preparation of silver nanoparticles and application in water-based conductive inks

We reported a simple, high yield and large-scale preparation method for silver nanoparticles. Silver nanoparticles with 8–13 nm in diameter were successfully synthesized by silver nitrate as raw material, sodium borohydride as reducing agent, dispersan-5040 (polycarboxylate sodium salt) as surface modifier in aqueous solution. The effects of sodium borohydride and dispersan-5040 on the morphologies of silver nanoparticles were investigated. Further, the conductive inks were prepared with as-synthesized silver nanoparticles as conductive fillers in the presence of deionized (DI) water and additives. The effects of conductive fillers and additives on the pH, conductivity, surface tension and viscosity of the inks were investigated. The conductive patterns were fabricated by inkjet printer and their performances were studied. The sheet resistances of the printed pattern with seven-layer was 1.2 [Formula: see text] when the printed pattern was heat-treated at 120[Formula: see text]C for 60 min. We succeeded in printing a simple conductive circuit on photographic paper, which can light three 0.06 W LED beads. The successful fabrication of the functional circuit proves the feasibility of the ink and provides some ideas for future paper-based circuits.

Water-based conductive ink for highly efficient electromagnetic interference shielding coating

Conductive inks are applied widely in electromagnetic interference (EMI) shielding coating, but the heavy use of organic solvents may cause safety issues and environment pollution. We demonstrated the preparation of an eco-friendly conductive ink that is composed of silver flakes, waterborne polyurethane, and fluorocarbon surfactant (Capstone FS-30), with deionized water as solvent. The conductive ink can be drop-deposited easily on polyethylene terephthalate film to develop a highly efficient EMI shielding coating that achieves an ultrahigh EMI shielding effectiveness (EMI SE) of 74.5 dB at only 10 μm thickness. The shielding coating exhibits sufficient flexibility to ensure an EMI SE retention up to 96%, even after 5000 bending–releasing cycles (bending radius of 2 mm), which reveals an excellent EMI shielding reliability. The shielding coating also possesses a mechanical fastness under ultrasonic treatment and a chemical durability to various organic solvents. These impressive characteristics make our conductive ink attractive for effective electromagnetic protection, especially in high integrated equipment and devices.

Cyclic Liquid-Phase Exfoliation of Electrically Conductive Graphene-Derivative Inks

Advances in electrically conductive inks and printing technology have enabled microelectrodes, chemical sensors, wireless radio frequency identification tags, and bioelectronic circuits to be fabricated on mechanically flexible polymers, paper, and bioresorbable silk. Although conductive polymer and metal-based inks have been used to build functional devices, these materials are often expensive and may involve complicated toxic chemical processes. Recent research has demonstrated that graphene (G), and its derivatives, can be used to create water-based conductive inks. In this paper, an environmentally friendly and cost-effective G-based conductive ink is proposed. The ink is created by using a nontoxic hydrophilic cellulose derivative, Carboxymethyl Cellulose (CMC), to facilitate liquid phase exfoliation and stabilization of naturally hydrophobic G sheets in DI water at high concentrations. It is demonstrated that recycling of nonexfoliated material can produce inks at comparable concentrations. Physical dimensions and defect status of exfoliated G sheets are characterized. Inkjet deposition of thin and thick films is achieved using a binary solvent system and electrical performance of resulting films is investigated. Film morphology is shown to be consistent between thin and thick films. Experiments have demonstrated that G-CMC films of <700 Ω/sq can be inkjet printed without use of dopants or dangerous solvents.

Custom tailoring of conductive ink/substrate properties for increased thin film deposition of poly(dimethylsiloxane) films

The creation of more robust biocompatible printed electronics devices requires an understanding of interactions between conductive inks and substrates to achieve desired printing and functional properties. In this study, we present a water-based conductive ink that can provide a readily achieved thin film deposition on a highly hydrophobic surface such as poly(dimethylsiloxane) (PDMS). We also show that surface treatments with atmospheric plasma can be utilized to tailor the surface energy of hydrophobic substrates to improve the deposition of inks not custom made for such applications. By using a tailored Ag nano-particle ink, we have successfully printed conductive traces onto a hydrophobic (PDMS) substrate without any surface modification. It was also shown that when introducing atmospheric plasma treatment to the PDMS substrate prior to printing with the tailored ink poor printing resulted. The proposed mechanism for the cause of this poor wetting and deposition is an adverse interaction between the ink and PDMS surface caused by surface oxidation resultant of plasma treatment. The results show that the generally accepted rule that a difference between the substrate and ink surface energy of 10 mN/m for good print quality does not necessarily hold true in the case of functional printing.

Optimization of the HgI2 Crystal Preparation for Application as a Radiation Semiconductor Detector

The effect of HgI2 crystal encapsulation using different polymer resins, with the intent of avoiding the oxidation of the crystal surface, was evaluated in this work. The crystal was purified and grown by the physical vapor transport (PVT) technique modified. Systematic measurements were carried out for evaluating the stoichiometry, structure orientation, surface morphology and impurity of the crystal grown. The purer region of the crystal grown was selected to be prepared as a radiation detector, applying water-based conductive ink contacts and copper wire on the crystal surfaces. After that, the crystal was encapsulated with a polymeric resin which insulates atmospheric gases, aiming to improve the stability of the HgI2 detector. Four resins were used for crystal encapslation and the performance of the detector depended on the composition of the resins used. Among the four resins studied to evaluate the influence of encapsulation on the performance of crystals, as a radiation detector, the best result of resistivity and energy spectrum was obtained for the resin #3 (50% - 100% of Methylacetate and 5% - 10% of n-butylacetate). The encapsulation of crystals with polymer resins, performed with the intent of avoiding the oxidation of the crystal surface, did not compromise the measurements and were fully capable of detecting the presence of gamma radiation. The stability of the encapsulated HgI2 crystal detector was of up to 78 hs, while the stability found for HgI2 detector no encapsulated was in order 3 ~4 hs.

Fabrication of nanoscale to macroscale nickel-multiwall carbon nanotube hybrid materials with tunable material properties

To utilize their superior properties, multiwall carbon nanotubes (MWNTs) must be manipulated and aligned end-to-end. We describe a nondestructive method to magnetize MWNTs and provide a means to remotely manipulate them through the electroless deposition of magnetic nickel nanoparticles on their surfaces. The noncovalent bonds between Ni nanoparticles and MWNTs produce a Ni-MWNT hybrid material (NiCH) that is electrically conductive and has an enhanced magnetic susceptibility and elastic modulus. Our experiments show that MWNTs can be plated with Ni for Ni:MWNT weight ratios of γ = 1, 7, 14 and 30, to control the material properties. The phase, atom-level, and morphological information from x-ray diffraction, energy dispersive x-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, dark field STEM, and atomic force microscopy clarify the plating process and reveal the mechanical properties of the synthesized material. Ni metalizes at the surface of the Pd catalyst, forming a continuous wavy layer that encapsulates the MWNT surfaces. Subsequently, Ni acts as an autocatalyst, allowing the plating to continue even after the original Pd catalyst has been completely covered. Raising γ increases the coating layer thickness from 10 to 150 nm, which influences the NiCH magnetic properties and tunes its elastic modulus from 12.5 to 58.7 GPa. The NiCH was used to fabricate Ni-MWNT macrostructures and tune their morphologies by changing the direction of an applied magnetic field. Leveraging the hydrophilic Ni-MWNT outer surface, a water-based conductive ink was created and used to print a conductive path that had an electrical resistivity of 5.9 Ω m, illustrating the potential of this material for printing electronic circuits.